We propose experiments in years 31 to 35 of a successful Program to explore the molecular basis of cell ransformation. The six participating laboratories will carry out investigations into the role of viral gene products, interacting cellular proteins, and mutagenesis in cell transformation. Dr. Miller will continue his studies on the mechanism of viral transactivators that disrupt herpesvirus latency. Dr. DiMaio will continue his analysis of the role of the human papillomavirus E6 and E7 oncogenes in maintaining the proliferation of human cervical cancer cells, with a particular emphasis on determining the molecular basis for induced senescence that occurs upon oncogene repression. Dr. Glazer in collaboration with Dr. DiMaio will develop novel nuclease-based strategies to interdict viral infection and improve the efficiency of gene targeting. In a project centered on mutagenesis, Dr. Sweasy will continue her analysis of cancer-associated DNA polymerase 13mutants and their ability to transform cells. A new Project Leader, Dr. Mothes will study the mechanism of retrovirus entry and spread in cells and infected animals. Finally, Dr. Steitz will continue her studies establishing the biochemical activities of tumor virus-encoded small RNAs and determining their effects on host cell function. In addition, an administrative core and two scientific cores (protein expression and purification, and viral vector) will provide essential services to the Program. This Program represents the significant commitment of the Yale University School of Medicine and the participating investigators to studies that will have direct relevance to understanding the cause of human cancer.